1. Field of the Invention
The present invention relates to a piston for an internal combustion engine, having a piston head with a piston crown, a circumferential top land, and a circumferential ring belt having ring grooves.
2. The Prior Art
Pistons for internal combustion engines are exposed to significant stresses during operation. In particular, the piston crown, the top land, and the piston ring that lies directly adjacent to the top land, including the ring groove that accommodates it, are exposed to particular mechanical and thermal stresses.
For this reason, the ring groove that lies adjacent to the top land is preferably provided with a ring insert. As a rule, the ring insert consists of an austenitic cast iron with lamellar graphite. These materials are also known under the name of NiResist materials. Such a ring insert is laid into the casting mold before a piston for an internal combustion engine is cast, and surrounded with the casting material. In the production of pistons from an aluminum alloy, the ring insert must be pre-treated, so that a bonding layer between the ring insert materials and the piston material is formed. For this purpose, the ring insert is generally Alfin-bonded, for example dipped into an aluminum/silicon melt, thereby forming a so-called Alfin layer, consisting of iron aluminides. This Alfin layer represents the desired bonding layer between the piston material and the ring insert materials.
This bonding layer is relatively rigid. Due to the special mechanical and thermal stresses that proceed from the combustion gases formed during ignition of the gaseous fuel/air mixture, there is therefore the risk that due to the mechanical stresses within the piston head, the bonding layer between the piston material and the ring insert materials will be subject to such great stress that the resulting tensile stress within the bonding layer will cause tearing of this layer. This causes the ring insert to loosen in the ring groove, and this, in the final analysis, results in engine damage.
The German Publication DE 39 08 810 A1 describes a piston for an internal combustion engine whose piston head is provided, below the ring belt, with two dead-end holes that run inward from the mantle of the piston skirt and extend parallel to the pin axis direction. In this way, the flow of force is guided into the width, in other words into the regions to the left and the right of the dead-end holes.
The circumstance that mechanical weakening of the piston head can take place due to the production of the dead-end holes is problematic in this connection.